1. Field of the Invention
The present invention relates to a solid-state imaging device, a method for manufacturing the same and an imaging apparatus.
2. Description of the Related Art
A solid-state imaging device of the related art will be described with reference to a schematic sectional view shown in FIG. 8.
As shown in FIG. 8, a photoelectric conversion portion (light-receiving portion) 112 converting incident light into signal charge is formed in a semiconductor substrate 111. The photoelectric conversion portion 112 is covered with an insulating layer 121 including, for example, an antireflection layer and a planarizing layer. The uppermost layer of the insulating layer 121 may be a planarizing layer, and a wiring portion 131 including a plurality of wiring layers and insulating interlayers filling the spaces between the wiring layers and between the conductor lines constituting the wiring layer is formed on the uppermost layer. A conductor line 135 of the wiring portion 131 is connected to a metal pad 137. The metal pad 137 is made of, for example, aluminum or an aluminum alloy.
The metal pad 137 is coated with a pad-coating insulating film 141 on the wiring portion 131.
An optical waveguide 151 is formed in the wiring portion 131 and the pad-coating insulating film 141 over the photoelectric conversion portion 112. The optical waveguide 151 is formed by forming a waveguide material layer 153 in a waveguide opening 133 formed in the insulating interlayers of the wiring portion 131 so as to fill the waveguide opening with a passivation layer 143 therebetween.
A color filter 171 and a condensing lens 181 are further formed on the optical waveguide 151 with a planarizing layer 161 therebetween. Such a structure is proposed in, for example, Japanese Patent Application No. 2006-332421.
The pad-coating insulating film 141 is formed to a thickness of 300 to 500 nm from the viewpoint of process simplicity and mass productivity.
The pad-coating insulating film 141 coats the metal pad 137 to prevent the metal pad 137 from being etched by etching for forming the waveguide opening 133.
Also, the pad-coating insulating film 141 prevents the direct contact of the metal pad 137 with a resist layer used as an etching mask for forming the waveguide opening 133. If the resist comes into contact with the metal pad 137, the metal pad 137 may deteriorate when the resist is reproduced. In particular, an aluminum or aluminum alloy metal pad 137 has a high risk of deterioration.
Therefore, the pad-coating insulating film 141 is preferably provided.
However, the pad-coating insulating film 141 is formed to a large thickness as described above. This increases the aspect ratio of the waveguide opening 133 to extend the entire length of the optical waveguide 151, consequently increasing the optical loss in the optical waveguide 151.
In addition, it may become difficult to fill the waveguide opening 133 with the waveguide material layer 153, and, consequently, voids (not shown) may be formed in the waveguide material layer 153.
A void in the optical waveguide 151 scatters incident light to reduce the quantity of the light reaching the photoelectric conversion portion 112, and thus result in reduced light-receiving sensitivity.
Furthermore, the increase in length of the optical waveguide 151 hinders oblique light from reaching the photoelectric conversion portion 112. Consequently, the sensitivity is reduced at an end of the angle of view, and thus the shading becomes worse.